The present invention relates to heaters, and more particularly, to gas-fired heaters, in which the combustion occurs at or near a combustion surface maintained at subatmospheric pressure The burner is operated at conditions which result in primarily convective heat transfer and reduced emissions of oxides of nitrogen (NO.sub.x), and carbon monoxide (CO).
Two embodiments of this invention are illustrated. One embodiment provides a novel and improved water heater in which improved performance is obtained by providing the combustion surface in a sealed combustion chamber maintained at subatmospheric pressure without the use of powered mechanical fans or blowers. A second embodiment provides a novel and improved space heater in which the combustion surface of the burner is maintained at subatmospheric pressure and is arranged for direct heat transfer to the surrounding space to be temperature conditioned.